Run flat pneumatic tire with shoulder cushion rubber layer loss tangent less than carcass coating rubber loss tangent

Abstract

There is provided a pneumatic tire having an aspect ratio of not less than 60 and considerably improving run flat durability as compared with the conventional type of the run flat tire, wherein at least one cushion rubber layer having a loss tangent lower than a loss tangent (tan delta) of a coating rubber for cords of a carcass ply is arranged between an end portion of a belt and a reinforcing rubber layer in a shoulder region and between mutually adjacent tire constitutional members. And also, when the carcass is comprised of plural plies, at least one ply is separated off in a zone beneath the belt, whereby the ride comfort against vibrations can be more improved.

Description

This invention relates to a pneumatic tire, and more particularly to a radial tire of so-called run flat type capable of running over a given distance at a state that an internal pressure becomes zero or is rendered into a slight pressure due to puncture or the like. Especially, it relates to a pneumatic tire having an excellent durability of run flat state (running at puncture state) for use in passenger cars, light trucks and small size trucks wherein a ratio of section height to section width (aspect ratio) is as relatively large as not less than 60.Radial tires of run flat type (hereinafter referred to as a run flat tire) are mainly used in vehicles wherein a load applied to the tire is relatively small such as passenger cars, light trucks, small size trucks and the like. In the run flat tire, it is required that when the tire is rendered into a flat state through puncture during not only the running on general-purpose roads but also the high-speed running on express ways, it is...

AI Technical Summary

Benefits of technology

And also, the tire 1 is provided at an inner face side of the turnup ply 6-1 as an innermost ply of the carcass 6 with a reinforcing rubber layer 9 having a crescent shape at a section thereof inherent to the run flat tire. The reinforcing rubber layer 9 is arranged in a region ranging from the vicinity of the bead core 5 through the sidewall portion 3 to the shoulder region of the tread portion 4 so that a central part in the radial direction of the tire is a thick part of 8.about.12 mm in maximum gauge and both end parts in the radial direction are tapered in order to stably support total weight of the vehicle during the running even at an internal pressure of zero and prevent separation off of the tire 1 from the rim used and prevent the breakage of the tire 1 and further hold the running stability even if rapid puncture is caused during the high-speed running at, for example, 80.about.120 km / h to make possible the support of high-speed running and the complete running over not less than 300 km under run flat condition without causing troubles.

In general, the reinforcing rubber layer is arranged in the sidewall portion as a structure of the tire capable of running at run flat state for controlling the bending of the tire at a state that the internal pressure is zero or substantially near to zero. As a result, such a tire tends to damage the ride comfort against vibrations in the usual running or at the inflation under the normal internal pressure as compared with the usual tire. For this purpose, when at least one ply is separated off beneath the belt to from a split ply as mentioned above, the flexibility is given to a crown portion of the carcass to absorb vibrations transmitted from a road surface with the crown portion, whereby the ride comfort against vibrations can be improved.

Problems solved by technology

However, this type of the tire is unavoidable in a point that the cost becomes higher and is frequently mounted onto an expensive grade of a vehicle supposing the high-speed running such as sport car, sport-type car or the like.

7. Finally, the thus improved conventional run flat tire can not attain the run flat runnable distance of not less than 300 km and support the high-speed running on the expressway as user's dema

And also, the means of incorporating the core into the rim has a problem firstly in the rim assembling property because the assembling of the tire onto a wheel is not easy.

Further, the big rise of weight in the tire and in the tire-wheel assembly is unavoidable and also unspring weight of the vehicle is largely increased to considerably damage the ride comfort of the vehicle against vibrations.

That is, there is a problem that these inconveniences become unsuitable in not only the high grade passenger cars but also the light tuck and small-size truck.

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